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Related Experiment Videos

Sequence evolution in bacterial endosymbionts having extreme base compositions.

M A Clark1, N A Moran, P Baumann

  • 1Microbiology Section, University of California, Davis, USA.

Molecular Biology and Evolution
|November 11, 1999
PubMed
Summary
This summary is machine-generated.

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Calibrating bacterial evolution rates is challenging. This study used aphid endosymbionts (Buchnera) and host fossils to date divergence, revealing faster bacterial evolution rates and reduced selection efficiency in Buchnera.

Area of Science:

  • Evolutionary Biology
  • Microbial Genetics
  • Molecular Evolution

Background:

  • Reconstructing bacterial evolution is hindered by the lack of dated ancestors for calibrating molecular clocks.
  • Vertically transmitted bacterial symbionts that cospeciate with hosts provide a reliable method for dating divergence events using host fossils.

Purpose of the Study:

  • To calculate bacterial evolutionary rates using dated divergence events of aphid hosts and their endosymbionts (Buchnera).
  • To compare evolutionary rates and selection efficiency between Buchnera and other bacteria like E. coli.

Main Methods:

  • Obtained gene sequences from Buchnera endosymbionts of two pairs of aphid hosts with known divergence times (50-70 MYA).
  • Calculated base substitution rates for neutral and selected sites in protein-coding genes and rRNA genes.

Related Experiment Videos

  • Analyzed synonymous and nonsynonymous substitution rates to infer selection efficiency.

    • Main Results:

    • Buchnera exhibited a homogeneous synonymous substitution rate across loci.
    • The synonymous rate in Buchnera was approximately double that of Escherichia coli-Salmonella typhimurium on an absolute timescale and fourfold higher on a generational timescale.
    • Nonsynonymous substitution rates were higher in Buchnera, suggesting reduced genome-wide selection efficiency.
    • Selection efficiency varied among Buchnera lineages, and a trend towards A+T-rich codons slowed or stopped in the last 50 million years.

    Conclusions:

    • Buchnera evolution rates are significantly higher than previously estimated on both absolute and generational timescales.
    • Reduced selection efficiency in Buchnera contributes to its distinct evolutionary trajectory and base composition.
    • The base composition of Buchnera appears to be approaching a limit imposed by selective constraints on protein function.